Abstract
KEYWORDS - Schlieren, Shadowgraph, Mie-scattering, gasoline, diesel
ABSTRACT
Three visualization methods, Schlieren, Shadowgraph, and Mie-scattering, were applied to compare diesel and gasoline spray structures. Fuels were injected into a high pressure/high temperature chamber under the same in-cylinder pressure and temperature condition of low load in a gasoline direct injection compression ignition (GDCI) engine. Two injection pressures (40 and 80 MPa), two ambient pressures (4.2 and 1.7 MPa), and two ambient temperatures (908 and 677 K) were use. The images from the different methods were overlapped to show liquid and vapor phases more clearly. Vapor developments of the two fuels were similar; however, different liquid developments were seen. At the same injection pressure and ambient temperature, gasoline liquid propagated more quickly and disappeared more rapidly than diesel liquid phase. At the low ambient temperature and pressure condition, gasoline and diesel sprays with higher injection pressures showed longer liquid lengths due to higher spray momentum. At the higher ambient temperature condition, the gasoline liquid length was shorter for the higher injection pressure. Higher volatility of gasoline is the main reason for this shorter liquid length under higher injection pressure and higher ambient temperature conditions. For a design of GDCI engine, it is necessary to understand the higher volatility of gasoline. In contrast to diesel spray under higher injection pressure for lower particulate matter (PM) emissions, gasoline spray under higher injection pressure leads to unstable combustion due to excessively lean mixture formation. For stable combustion in a GDCI engine, 20 MPa injection pressure was suitable under low load condition and this was confirmed experimentally in a GDCI engine.